FIX 解决forked项目删除后，fork user没有关联删除的bug

app/models/fork_user.rb

@@ -1,4 +1,6 @@
 class ForkUser < ApplicationRecord
-  belongs_to :project 
+  belongs_to :project
   belongs_to :user
+  belongs_to :fork_project, class_name: 'ForkUser', foreign_key: :fork_project_id
+
 end

app/models/project.rb

@@ -18,6 +18,7 @@ class Project < ApplicationRecord
   has_many :project_trends, dependent: :destroy
   has_many :watchers, as: :watchable, dependent: :destroy
   has_many :fork_users, dependent: :destroy
+  has_many :forked_users, class_name: 'ForkUser', foreign_key: :fork_project_id, dependent: :destroy
   # has_many :commits, dependent: :destroy
 
   has_one :project_score, dependent: :destroy